1. Field of the Invention
This invention relates to a semiconductor device and a manufacturing method thereof and, more particularly, to a semiconductor device comprising a CMOS (Complementary Metal Oxide Semiconductor) device, a memory device and the like on the same substrate and a manufacturing method thereof.
2. Description of the Related Art
Recently, a faster semiconductor device and a lower power consumption thereof have been increasingly required. For example, faster operations of a CMOS device provided in a semiconductor device and lower power consumption thereof have been achieved by a finer device structure.
However, as the device structure becomes finer, a pattern smaller than an exposure wavelength needs to be formed by lithography. For this reason, an adequate margin of process can hardly be maintained in the lithographic step. Thus, there is a limit to satisfying the requirement of faster semiconductor device and a lower power consumption thereof by the finer device structure.
To improve a current driving power of the MOS transistor, development of providing a strained-Si layer on a semiconductor substrate and forming a MOS transistor on the strained-Si layer has been carried out. In the strained-Si layer, a banded structure of Si is varied by applying a tensile strain to Si.
The strained-Si layer is formed by forming, for example, a Si1−xGex layer (hereinafter called a SiGe layer) having a greater lattice constant than Si on a semiconductor substrate and forming a Si layer thereon by epitaxial growth, to apply a sufficiently great tensile strain to Si. If a MOS transistor is formed on the strained-Si layer thus formed, carrier mobility is improved.
In accordance with high integration of a semiconductor device, a semiconductor device having a CMOS device with a memory device or an analog device on the same substrate is manufactured. If a semiconductor substrate having a strained-Si layer is used in such a semiconductor device, the carrier mobility of the CMOS device can be improved as explained above.
In the memory device or analog device, however, current leak or noise occurs due to influences of the strained-Si layer whose lattice constant is made greater than that of Si and the SiGe layer whose lattice constant is greater than that of Si. The characteristics of the memory device or the analog device are thereby deteriorated.
Moreover, if a small-leak type transistor or capacitor in which the current leak from a capacitor dielectric film or junction leak causes problems is formed on a strained-Si layer, the device characteristics are deteriorated. This is serious for the analog device or DRAM (Dynamic Random Access Memory) including such a device.
As for a related technique of this kind, a CMOS device capable of compensating for high charge carrier mobility by using strained silicon is disclosed (see Jpn. Pat. Appln. KOKAI Publication No. 10-107294).